Sulfenic acids in the carbohydrate field. An example of straightforward access to novel multivalent thiosaccharides

Both anomers of O-protected 1-thio-D-gluco- and -D-mannopyranoses were selected to provide the substrates for developing a smooth and general methodology that gives access to anomeric glycosulfoxides. The behavior of the corresponding beta-D-galactopyran derivatives was also investigated. 2-{1-[(2,3,4,6-Tetra-O-acetyl-beta-D-glucopyranosyl)sulfinyl](1-methyl)ethyl}malonic acid diethyl esters 4 were thermolyzed in refluxing dichloromethane for generating 2,3,4,6-tetra-O-acetyl-beta-Dglucopyranose- 1-sulfenic acid (8), in the presence of 2-propynyl beta-D-glucopyranoside tetraacetate (32). The syn-addition of transient 8 onto the triple bond of 32 furnished 2-[(2,3,4,6-tetra-O-acetyl- beta-D-glucopyranosyl)sulfonyl]-2-propenyl beta-D-glucopyranoside tetraacetate (34), after m-CPBA oxidation of the corresponding sulfinyl epimeric mixture 33. This synthetic pathway appears particularly attractive since it represents an example of a mild and versatile approach to thiodisaccharides of foreseeably significant biological behavior. Various carbohydrate-derived sulfenic acids, different in glycosyl moiety and sulfenic function positioning, and various alkynylated carbohydrates can be adopted as combining units in the synthesis of alkene-linked multivalent thiosaccharides.